Electrical appliances such as ceiling fans and lights are designed to be powered by one active (hot) conductor carrying AC current and a neutral return line. Some appliances have multiple functions which may be manually selected by the user.
A ceiling fan which incorporates a light fixture is a multiple function electrical load. Some ceiling fans may be controlled to operate at different speeds, and some light fixtures may be controlled to operate at different light intensity levels.
It is sometimes desirable to replace an overhead light fixture with a combination ceiling fan and electrical light. Power to the fan and light combination is controlled through an on/off wall switch, with AC power being conducted to the fan and light through existing wiring. The on/off wall switch controls power to the fan and light, and other controls such as speed control, direction of rotation and brightness may be provided by manual switches located on the fan assembly and on the light assembly.
In some instances, controls for operating an overhead ceiling fan and light fixture have been incorporated as a part of a wall switch. Such arrangements require the installation of additional wiring between the wall switch and the existing ceiling fixture. It is generally desirable to be able to control the application of power to the combined fan and light from the wall switch location using the existing wiring between the wall switch location and the ceiling fixture for separately controlling and operating the ceiling fan through a range of different speeds, and also for controlling and operating the light fixture through a range of different light levels.